1. Field of the Invention
The present invention relates to a supporting mechanism in which a rotatable operation ring is rotatably supported by a cylindrical member in a lens barrel.
2. Description of Related Art
In a known lens barrel, there are various rotating rings including a zooming ring, a focusing ring, a diaphragm setting ring, etc. These rotating operation rings must be correctly fitted in or on respective support members without any play, so that the rotating rings can be smoothly rotated with an appropriate rotation torque while an operator physically feels the rotational movement thereof. The precise fitting, the easy adjustment of the rotational torque and the provision of a feeling of the rotational movement are particularly important for the zooming ring, since the latter is rotated so as to independently move at least two front and rear variable power lens groups in the optical axis direction by a relatively large displacement.
To this end, in a conventional zooming ring, the rotational torque is adjusted by an adjustment of a clearance between a cam groove formed on a cam ring, which is rotated together with the zooming ring and a roller fitted in the cam groove, and a selection of lubricant to be applied to the rotating and fitting portion of the cam ring. It is also known to provide a biasing member between the zooming ring and the stationary cylindrical member to bias the zooming ring in the radial direction to thereby adjust the play of the rotating and fitting portion and the rotational torque. However, the adjustment of the clearance between the cam groove and the roller fitted therein and the selection of the lubricant can not ensure a stable operation of the action of the zooming ring. Moreover, the biasing member in the radial direction sometimes conversely increases the play of the fitting portion.